resolve nested model classes in HomeHelper#metadata

`metadata(cls)` did a bare `LinkedData::Models.const_get(name)`, so
requests like `GET /metadata/Reply` blew up with
`NameError: uninitialized constant LinkedData::Models::Reply` —
`Reply` lives under `LinkedData::Models::Notes`, not at the top level.
`routes_by_class` already has sub-module search for the same reason;
`metadata` was missing the mirror.

Extract a small `resolve_model_class(name)` helper that tries the
top-level lookup first and falls back to scanning
`LinkedData::Models.constants` for the name, matching the behavior of
`routes_by_class`. This restores `GET /metadata/Reply` and any other
nested model class (e.g. `Users::Role`, `Users::NotificationType`).

test_metadata_route_resolves_submodule_class now passes.

Author: alexskr

helpers/home_helper.rb

@@ -42,12 +42,24 @@ def resource_collection_link(cls)
 
       def metadata(cls)
         unless cls.is_a?(Class)
-          cls = cls.singularize
-          cls = LinkedData::Models.const_get(cls)
+          cls = resolve_model_class(cls.singularize)
         end
         metadata_all[cls]
       end
 
+      # Resolve a model class by bare name, checking LinkedData::Models first
+      # and falling back to sub-modules (e.g. LinkedData::Models::Notes::Reply
+      # for "Reply"). Mirrors the sub-module search in `routes_by_class`.
+      def resolve_model_class(name)
+        LinkedData::Models.const_get(name)
+      rescue NameError
+        LinkedData::Models.constants.each do |const|
+          sub_cls = LinkedData::Models.const_get(const).const_get(name) rescue nil
+          return sub_cls if sub_cls.is_a?(Class)
+        end
+        raise
+      end
+
       def sample_objects
         ontology = LinkedData::Models::Ontology.read_only(id: LinkedData.settings.rest_url_prefix+"/ontologies/BRO", acronym: "BRO")
         submission = LinkedData::Models::OntologySubmission.read_only(id: LinkedData.settings.rest_url_prefix+"/ontologies/BRO/submissions/1", ontology: ontology)